1. Field of the Disclosure
The present disclosure relates to an anti-reflective coating polymer used in a photolithography process, which is one process for fabricating a semiconductor device, a method for preparing the anti-reflective coating polymer, and an anti-reflective coating composition comprising the anti-reflective coating polymer. More specifically, the present disclosure relates to a top anti-reflective coating polymer usable in immersion lithography for the fabrication of a sub-50 nanometer (nm) semiconductor device, a method for preparing the top anti-reflective coating polymer, and a top anti-reflective coating composition comprising the top anti-reflective coating polymer.
2. Description of the Related Technology
Photolithography is a process for the transfer of a semiconductor circuit pattern formed on a photomask to a wafer, and is one of the most important processes in determining the fineness and integration density of circuits in the fabrication of semiconductor devices.
In recent years, as the integration density of semiconductor devices has increased, new techniques have been developed that are adapted to the fine processing required in the fabrication of semiconductor devices. Under these circumstances, there is an increasing need for a fine processing technique in a photolithography process. That is, as the circuit line widths become finer and finer, the use of short-wavelength light sources for illumination, such as KrF, ArF, F2 and EUV excimer lasers, and high numerical aperture lenses are required. EUV, F2, ArF and KrF lasers in this order are preferentially used as light sources because of their short wavelength.
Particularly, a number of studies on the development of sub-50 nanometer (nm) devices have been actively undertaken. In response to these studies, recent attention has been directed toward the development of suitable processing equipment and materials associated with the use of F2 and EUV as exposure light sources. Technical solutions for the use of F2 are somewhat satisfactory, but there are the following problems: 1) high-quality CaF2 is difficult to produce on an industrial scale within a short time, 2) because soft pellicles are likely to be deformed upon exposure to light at 157 nm, their life is short, and 3) hard pellicles incur considerable production costs, and are difficult to produce on a commercial scale due to their nature of light refraction.
On the other hand, since suitable light sources, exposure equipment, and masks are required to use EUV lasers, they are not yet suitable for practical use. Accordingly, the formation of finer high-precision photoresist patterns by using a photoresist adapted to the use of an ArF excimer laser have now become a key technical task. Under these circumstances, immersion lithography has recently drawn attention.
Dry lithography is a currently used lithography process, and is an exposure system wherein air is filled between an exposure lens and a wafer. In contrast to dry lithography, immersion lithography, which corresponds to an NA scaling technique, is an exposure system wherein water is filled between an exposure lens and a wafer. Since water (refractive index (n)=1.4) is used as a medium for a light source in the immersion lithography, the NA is 1.4 times larger than that in the dry lithography using air (refractive index (n)=1.0). Accordingly, immersion lithography is advantageous in terms of its high resolution.
A problem encountered with the fabrication of a sub-50 nm semiconductor device is that alteration of the critical dimension (CD) of a photoresist pattern inevitably takes place during a process for the formation of an ultra fine pattern. These alterations arise from standing waves, reflective notching due to the optical properties of a underlying layer on an overlying photoresist and due to variation in the thickness of the photoresist, and diffracted and reflected light from the underlying layer. To prevent the reflected light from the underlying layer, a light-absorbing material, called an “anti-reflective coating”, at a wavelength band of light used as an exposure light source is introduced between the underlying layer and the photoresist. A bottom anti-reflective coating interposed between the underlying layer and the photoresist has been used to date. With the recent increase in the fineness of the photoresist patterns, a top anti-reflective coating (TARC) has also been introduced in order to prevent the photoresist pattern from being disrupted by both reflected and diffracted light. Specifically, as the miniaturization of semiconductor devices makes photoresist patterns extremely fine, the use of a bottom anti-reflective coating alone cannot completely prevent the patterns from being disrupted by scattered reflection. Accordingly, a top anti-reflective coating has been introduced to prevent the disruption of the patterns.
However, because conventional top anti-reflective coatings for use in dry lithography are water-soluble (in the case of using KrF or ArF laser), they cannot be applied to immersion lithography. In other words, because water is used as a medium for a light source in immersion lithography, it easily dissolves the conventional top anti-reflective coatings.
Accordingly, an ideal top anti-reflective coating for use in immersion lithography must satisfy the following requirements: 1) the top anti-reflective coating must be transparent to a light source; 2) the top anti-reflective coating must have a refractive index between 1.4 and 2.0, depending on the kind of an underlying photosensitive film (i.e. photoresist) to be used; 3) when the top anti-reflective coating composition is coated on an underlying photosensitive film, it must not dissolve the photosensitive film; 4) the top anti-reflective coating must not be soluble in water upon light exposure; 5) the top anti-reflective coating must be soluble in a developing solution; and 6) the top anti-reflective coating must enable the formation of a vertical pattern.
The above-mentioned stringent requirements make the development of a suitable top anti-reflective coating for use in immersion lithography difficult. Particularly, a new concept top anti-reflective coating composition is needed to satisfy the requirements of 6). Thus, there exists a need for the development of a top anti-reflective coating for use in immersion lithography which is water-insoluble and enables the formation of a vertical pattern upon formation of a semiconductor pattern.